Methods for reducing the cost to maintain a fleet of repairable systems

A problem that is receiving increased attention within government and industry is the cost to maintain fleets of repairable systems. As a fleet ages attention is often directed toward identifying major cost drivers and instituting various changes to reduce the ownership cost. These changes may include technology design modifications to increase reliability, or a change in support strategies. In both cases the repair and overhaul policies must be considered and established. These policies significantly affect the operating costs, reliability, sustainment, and effectiveness of the entire fleet. Because the system, subsystems, and in most cases the line replaceable units (LRUs) are all repaired upon failure, these policies must also address the issue of overhaul versus repair on these units. The economic life of a repairable item is usually defined as that overhaul time that will minimize the item´s long-term life cycle cost. However, if the item is wearing out, the reliability may be deteriorating beyond a desired limit at the economic life. Useful life is defined as the minimum of the economic life overhaul time and that point where reliability is less than a required limit. This paper discusses methods for estimating the useful life for a fleet of repairable systems, and presents a model and procedures for addressing in-service reliability growth.